Why are so many of these sentences weird? I was doing dutch and got the sentence "I am not a banana!" and also "Luis eats spiders" in spanish.
I think that's an important point – if all the sentences were of the type 'where is the hotel' then there will be greater tendency to just guess them.
Also, the publicity they get from sentences being shared on social media helps them. For example: Zooey Deschanel (New Girl) tweeting about 'You are easy' etc. In fact the job advert for Duolingo Stories/Bots had a reference to this aspect.
I was just listening to a Podcast on the language instruction system called TPRS ("Teaching Proficiency through Reading and Storytelling"). Using unexpected sentences was explicitly mentioned as a useful part of the system. As others have said, it's because they're more memorable.